Exposure apparatus and method

ABSTRACT

An exposure apparatus and method wherein a mask is illuminated with light and light one of transmitted through and reflected from the illuminated mask is imaged onto a substrate. At least during imaging, transmission of light one of transmitted and reflected from the illuminated mask is partially inhibited. More particularly, a spatial filter is utilized for inhibiting at least a portion of O-order diffraction light.

This is a continuation of application Ser. No. 07/846,158, filed Mar. 5,1992 now U.S. Pat. No. 5,329,533 issued Jul. 12, 1994.

BACKGROUND OF THE INVENTION

The present invention relates to an exposure method and apparatustherefor, an exposure system and a mask circuit pattern inspectionsystem, which eliminate an influence of interference light generated inan extremely fine circuit pattern formed on a mask, so that an image isformed with a high resolving power on a substrate through a projectionlens and exposed and, further, wherein the light source is an excimerlaser light source.

In the manufacture of an LSI, a circuit pattern on a mask is exposed andtransferred onto a wafer to form a fine circuit pattern on the wafer.However, to cope with the need of high integration of LSI, the circuitpattern transferred onto the wafer tends to be an extremely finepattern, which constitutes a resolution limit of an imaging opticalsystem.

In view of the foregoing, various techniques have been developed inorder to transfer an extremely fine circuit pattern.

For example, there is a method for exposure using X-rays such as SOR(Synchrotron Organized Resonance) light. There is a further method whichuses an EB (Electron Beam) exposure machine. Furthermore, there isanother method using an excimer laser disclosed in "Excimer LaserStepper for Sub-half Micron Lithography, Akikazu Tanimoto, SPIE, Vol.1088 Optical Laser Microlithography 2 (1989)" or Japanese PatentLaid-Open No. 57(1982)-198631.

A theoretical analysis of partial coherent imaging is introduced in"Stepper's Optics (1), (2), (3) and (4)" (Optical Technical Contact:Vol. 27, No. 12, pp. 762-771, Vol. 28, No. 1, pp. 59-67, Col. 28, No. 2,pp. 108-119, Vol. 28, No. 3, pp. 165-175).

Also, Japanese Patent Unexamined Publication No. 3-27516 describes anexample in which a spatial filter is used to improve a resolving power.

Further, a phase shifter method for modifying a mask to improve aresolving power is known from Japanese Patent Publication No.62(1987)-50811. According to this phase shifter method, light from aneighboring pattern is made to interfere, thereby enhancing theresolving power, which is realized by providing a film (a phase shifter)with phases alternately deviated through π so that phases of adjacentpatterns are inverted. However, the prior art known from theaforementioned Patent Publication No. 62(1987)-50811 has a problem inthat an arrangement of the phase shifter is difficult, and themanufacture of a mask provided with the phase shifter is difficult.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an exposure method andan apparatus therefor so that an extremely fine white and black circuitpattern formed on a mask can be transferred onto a substrate with aresolving power equal to or higher than a phase shifter, while solvingthe aforementioned problem noted with respect to the prior art.

It is a further object of the present invention to provide an exposuremethod and system, and particularly an excimer exposure method andsystem, in which data of a transferred pattern on a substrate actuallytransferred by an exposure apparatus can be confirmed through simulationby arithmetic processing.

It is another object of the present invention to provide a mask circuitpattern inspection system in which even in the case where an extremelyfine circuit pattern formed on a mask is different from a patterntransferred onto a substrate, the extremely fine circuit pattern formedon the mask can be inspected with high accuracy.

The aforesaid problem can be solved by the present invention whichprovides an exposure apparatus or exposure method comprising anilluminating arrangement, such as an excimer laser light source, havingcoherent property to a certain degree, an imager for imaging light inwhich a mask (including a reticle) illuminated by the illuminatingarrangement is imaged onto a wafer, and a shield for shielding at leasta part of the O-order diffraction light out of light which transmitsthrough or reflects from the mask.

The present invention further provides an excimer exposure apparatuswherein a spatial filter shields an area corresponding to the NA of theilluminating arrangement.

Furthermore, the present invention provides an excimer exposureapparatus wherein the illuminating arrangement comprises an integratorand a spatial filter.

Moreover, the present invention provides an excimer exposure apparatuswherein the mask has a circuit pattern formed to have a line width whichis substantially 1/2 of an imaging resolving power.

The present invention also provides a projection type exposure apparatusand method comprising an illuminating arrangement for substantiallyuniformly applying ring-like diffused illumination formed from a numberof imaginary point sources to a mask in an exposure area, and areduction projection lens having an optical eye which shields at least apart of the O-order diffraction light or low-order diffraction light outof light which transmits through the mask substantially uniformlydiffused and illuminated by the illuminating arrangement and imaging acircuit pattern formed on the mask onto a substrate in the exposurearea, wherein the circuit pattern formed on the mask is sequentiallyexposed on the substrate by step-and-repeat processing.

The present invention further provides an excimer exposure method whichincludes the steps of illuminating a mask formed with a circuit pattern,shielding at least a part of the O-order diffraction light out of lightwhich transmits through or reflects from the circuit pattern of theilluminated mask, imaging the light by an imager, and transferring theimaged light onto a substrate.

Furthermore, the present invention provides an excimer exposure methodwherein the minimum line width of the circuit pattern on the mask isformed by being suited to an imaging resolving power of the imager.

Moreover, the present invention provides an excimer exposure methodwherein the mask has a circuit pattern formed to have a line width whichis substantially 1/2 of the imaging resolving power.

The present invention further provides an excimer exposure methodwherein the circuit pattern on the mask is formed to have a line widthwhich is substantially 1/2 of the imaging resolving power, and in a widecircuit pattern when transferred onto a substrate, a transmissionportion on the mask is formed of a line and space having a pitch ofsubstantially 1/2 to 1/3 of the imaging resolving power or a latticepattern.

The present invention further provides an excimer exposure method whichincludes the steps of dividing a circuit pattern formed on a mask into afine pattern portion and a large pattern portion, imaging them by animager and transferring the same onto a substrate.

The present invention also provides an excimer exposure system includinga mask data converter for converting and producing data of a mask fromdata, and a calculator for applying arithmetic processing based on atransmission function substantially equivalent to an imager fortransferring a circuit pattern formed on the mask using excimer laserlight with respect to mask data obtained from the mask data converter tocalculate data of the transferred pattern onto a substrate.

The present invention additionally provides a mask circuit patterninspection system including a mask data converter for converting andproducing data of a mask from wiring data, a calculator for applyingarithmetic processing based on a transmission function substantiallyequivalent to an imager for transferring a circuit pattern formed on themask using excimer laser light with respect to mask data obtained fromthe mask data converter to calculate data of a transferred pattern on awafer, an inspection device including an illuminating arrangement forilluminating a mask with the excimer light, an imager for imaging lightwhich transmits through or reflects from a mask illuminated by theilluminating arrangement to a detection position, the imager having atransmission function substantially equivalent to that of thefirst-mentioned imager, and a light receiver for receiving an imagingcircuit pattern imaged on the detection position to obtain an imagesignal, and a comparator for comparing an image signal obtained from thelight receiver of the inspection device with data of a transferredpattern on a wafer calculated by the calculator.

In an exposure apparatus using excimer laser light, for example, thecontrast of a circuit pattern transferred onto a substrate is degradedbecause diffraction light cannot be sufficiently taken into an opening(pupil) of the imager. Light is diffracted according to the usingwaveform and the dimension of the circuit pattern from the circuitpattern on the mask. At that time, in the case where a circuit patternis extremely fine, a diffraction angle becomes large, and intensity ofdiffracted light also increases. As the result, light does not enter anopening of the imager (projection lens) used for transfer, whichconstitutes the cause for degrading the resolving power.

In order to minimize the loss of the diffracted light, it iscontemplated that the wavelength is shortened to reduce diffractioncomponents as in an excimer laser stepper or the NA of the imager(projection lens) is increased so as to receive diffraction light asmuch as possible.

On the other hand, according to the present invention, with a view to aphenomenon in which less components of diffraction light from a circuitpattern on a mask is received into imager (projection lens) whereas allcomponents (O-order diffraction light) not diffracted from the circuitpattern on the mask are received therein, the O-order diffraction lightalone in a large amount of light necessary for imaging is received intothe imager (projection lens), and less diffraction light components isrelatively received into the imager (projection lens). From a viewpointof this, at least a part of the O-order diffraction light is shieldedthereby to relatively improve a balance in quantity of light between thediffraction light emitted out of the imager (projection lens) and theO-order diffraction light and to improve the contrast of an extremelyfine circuit pattern formed on the mask to be imaged and transferredonto the substrate through the imager (projection lens), thus realizingthe exposure with high resolving power.

Particularly, in the present invention, there are provided anilluminating arrangement for substantially uniformly applying aring-like diffused illumination formed from a number of imaginary pointsources to a mask in an exposure area, and a reduction projection lenshaving an optical aye which shields at least a part of the O-orderdiffraction light or low-order diffraction light out of light whichtransmits through the mask substantially uniformly diffused andilluminated by the illuminating arrangement and imaging a circuitpattern formed on said mask on a substrate in the exposure area. Withthis structure, an extremely fine circuit pattern formed on the mask isimaged and transferred onto the substrate through the reduced projectionlens to improve the contrast, thus realizing an exposure of highresolving power.

It is noted that although the present invention is hereinafter describedin relation to use of excimer laser light, the present invention is notlimited to a projection type exposure method using excimer laser light.

These and further objects, features and advantages of the presentinvention will become more obvious from the following description whentaken in connection with the accompanying drawings which show forpurposes of illustration only, several embodiments in accordance withthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) and (b) show a diffraction phenomenon of light by a circuitpattern formed on a mask for explaining the principle of the presentinvention.

FIGS. 2(a) and (b) are views for explaining the principle of the presentinvention.

FIG. 3 is a view for further explaining the principle of the presentinvention.

FIG. 4 is a schematic perspective view showing one embodiment of anexposure system in a reduction projection exposure device according tothe present invention.

FIG. 5 is a sectional view showing a relationship between a light sourcespatial filter and an imaging filter in an exposure system according tothe present invention.

FIG. 6 is a sectional view showing a relationship of an imaging space inan exposure system according to the present invention.

FIGS. 7(a) and (b) are views showing an imaging relationship of acircuit pattern on a mask in a conventional reduction projectionexposure device.

FIG. 8 is a graph showing response function of the system in accordancewith the present invention.

FIG. 9 is a view for explaining the relative function between the shapeof the light source and the shape of the pupil surface according to thepresent invention.

FIG. 10 is a view for explaining the relative function between the shapeof the light source and the shape of the pupil surface according to theprior art.

FIGS. 11(a)-(c) are views for explaining the calculating method of therelative function between the shape of the light source and the shape ofthe pupil surface.

FIG. 12 is a view for explaining the calculating method of the relativefunction between the shape of the light source and the shape of thepupil surface.

FIG. 13 is a view showing the calculated result of OTF according to thepresent invention.

FIG. 14 is a view showing the focal depth according to the presentinvention.

FIGS. 15(a)-(b) are views for explaining the effect of a ring-like lightsource and a ring-like filter.

FIGS. 16(a)-(b) are views showing a ring-like filter.

FIGS. 17(a)-(d) are views showing a ring-like light source and aring-like filter.

FIGS. 18(a)-(b) show intensity distributions of a ring-like light sourceand a ring-like filter in accordance with an embodiment of the presentinvention.

FIGS. 19(a)-(b) intensity distributions of a ring-like light source anda ring-like filter in accordance with another embodiment.

FIGS. 20(a)-(c) show the embodiments of a ring-like light source and aring-like filter.

FIG. 21 shows OTF curves.

FIG. 22 shows other OTF curves.

FIG. 23 shows another embodiment of a ring-like light source and aring-like filter.

FIG. 24 is a view showing a block diagram of an embodiment of a lightsource.

FIG. 25 show one embodiment of an integrator.

FIG. 26 show another embodiment of a ring-like light source and aring-like filter.

FIG. 27 is a structural view showing one embodiment of the wholeexposure system according to the present invention.

FIG. 28 is a perspective view showing an integrator having an lightsource spatial filter in an exposure system according to the presentinvention.

FIG. 29 is a perspective view showing another embodiment of anintegrator having a light source spatial filter in an exposure systemaccording to the present invention.

FIG. 30 is a perspective view showing an embodiment of an imaging lenshaving an imaging spatial filter in an exposure system according to thepresent invention.

FIG. 31 is a perspective view showing another embodiment of an imaginglens having an imaging spatial filter in an exposure system according tothe present invention.

FIG. 32 is a plan view showing a relationship between a light sourcespatial filter of one embodiment and an imaging spatial filter of oneembodiment according to the present invention.

FIG. 33 is a plan view showing a relationship between a light sourcespatial filter of another embodiment and an imaging spatial filter ofanother embodiment according to the present invention.

FIG. 34 is a plan view showing a light source spatial filter of afurther embodiment and an imaging spatial filter of a further embodimentaccording to the present invention.

FIG. 35 is a plan view showing a light source spatial filter of anotherembodiment and an imaging spatial filter of another embodiment accordingto the present invention.

FIG. 36 is a plan view showing a relationship between a light sourcespatial filter of yet another embodiment and an imaging spatial filterof yet another embodiment according to the present invention.

FIGS. 37(a) and (b) show a plan view and a sectional view of one exampleof a wafer pattern transferred on a wafer.

FIGS. 38(a) and (b) show a plan view and a sectional view of a modifiedwafer pattern transferred onto a wafer according to the presentinvention.

FIG. 39(a) and (b) is a plan view and a sectional view of one example ofa mask pattern for obtaining the wafer pattern shown in FIG. 37according to the present invention.

FIGS. 40(a) and (b) show a plan view and a sectional view of one exampleof a mask pattern for obtaining the wafer pattern shown in FIG. 38according to the present invention.

FIGS. 41(a)-(d) show various modes of mask patterns according to thepresent invention.

FIGS. 42(a) and (b) show a view showing a relationship contrast on awafer and δ, ε in connection with a spatial filter according to thepresent invention.

FIG. 43 shows a relationship between contrast on a wafer and σ inconnection with a spatial filter according to the present invention.

FIG. 44 is a view showing a relationship between a line width of acircuit pattern on a mask and contrast on a wafer according to thepresent invention.

FIG. 45 shows a relationship between a pitch of a circuit pattern on amask and contrast on a wafer according to the present invention.

FIG. 46 is a plan view showing one example of a circuit pattern on amask according to the present invention.

FIG. 47 shows a transfer result of a circuit pattern of FIG. 46according to the present invention.

FIG. 48 shows a relationship between a pitch of an extremely finecircuit pattern formed on a mask and contrast on a wafer according tothe present invention.

FIG. 49 shows a relationship between a focal depth and contrastaccording to the present invention.

FIG. 50 is a block diagram arrangement of another embodiment of theentire exposure system using an excimer laser light source according tothe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, the principle of the present invention will be described withreference to FIGS. 1 to 7. In the present invention, a circuit patternon a mask is transferred with an improved contrast rather than the artin which the circuit pattern is faithfully transferred onto a substrateby the imager (projection lens). Namely, in projection exposure, therequirement that "a circuit pattern is transferred accurately" is notalways necessary the present invention is based on a new technicalfeature that "a circuit pattern desirably formed on a substrate (wafer)is better transferred with high contrast".

FIG. 1(a) is a sectional view of a mask 100 in which a mask circuitpattern 104 is formed on a glass substrate 101 by chrome 102. In FIG.1(b), a waveform 301 shows, with respect to the mask circuit pattern104, a signal distribution of an imaging pattern imaged onto a substrate(wafer) 200 by a projection and exposure device 3000 as shown in FIGS. 4to 6. The waveform 301 is divided into a waveform 302 by the O-orderdiffraction light and a waveform 303 by higher order diffraction light.In the case where the mask circuit pattern 104 is a fine circuit pattern105 as shown in FIG. 1(a), the waveform 301 detected is small incontrast AM/AV since the waveform 303 by the higher order diffractionlight is small as compared with the O-order diffraction light. Since thecomponent of the waveform 302 can be removed by shielding the O-orderdiffraction light, the detected waveform is high in contrast as in thewaveform 302.

A further principle of the present invention will be describedhereinbelow. That is, the present invention is intended to invert phasesof circuit patterns adjacent to each other on the mask (by π) withoutusing a phase film. In the case where a shield portion between circuitpatterns 321 and 323 adjacent to each other of a mask (reticle) 100 isnarrow as shown in FIGS. 2 and 3, a completely complementary figureresults, and in the case where the shield portion has a finite width, anapproximately complementary figure results. The circuit patterns 321 and323 adjacent to each other of the mask (reticle) 100 are equal in lightintensity except at one central point (O-order diffraction light) with aphase deviated by π, in a Fraunhofer's diffraction image under theprinciple of Babinet, in a diffraction image surface 3203 by an imagingoptical system (projection lens) 3201. In the diffraction image surface3203 and in diffraction patterns other than the O-order diffractionlight, light from the circuit patterns 321 and 323 is inverted in phase(deviated by π), and at least a part of the O-order diffraction light isshielded by a shield plate 324 (an imaging spatial filter 3302) on thediffraction pattern (diffraction image surface), whereby light imagedonto a substrate 200 surface (an imaging surface) is equal to that lightfrom the patterns adjacent to each other whose phases are inverted(deviated by π) and an extremely fine circuit pattern with high contrast(an extremely fine circuit pattern of 0.1 μm or less on a wafer) can betransferred onto a substrate 200.

More specifically, as shown in FIG. 2 or 3, at least a O-order part ofthe diffraction light is shielded by the shield plate 324 (imagingspatial filter 3302) on the diffraction image surface whereby only thediffraction light with an inverted phase reaches the imaging surface andtherefore, it appears as if a phase film is formed on the mask as viewedfrom the imaging surface. As a result, a circuit pattern which is thesame as the phase shifter method is imaged onto the wafer, and in termsof intensity distribution of the imaging surface, an extremely finecircuit pattern with high contrast is obtained on the wafer 200 ascompared with the case of a conventional reduction projection exposureshown in FIG. 7.

FIG. 7 is a view for explaining the case of the conventional reductionprojection exposure, in which images of fine circuit patterns 321 and323 adjacent to each other are high in contrast in the imaging surface.In short, in case of the reduction projection exposure according to thepresent invention, an extremely fine circuit pattern with high contrast(an extremely fine circuit pattern of 1 μm or less on a wafer) istransferred and exposed on the imaging surface as shown in FIGS. 2 and 3as compared with the conventional reduction projection exposure shown inFIG. 7.

The example shown in FIG. 4 will be described hereinafter by way ofexpressions (formulae). In the example shown in FIG. 4, light from amercury lamp 3101 is condensed at a light source spatial filter 3301 bya condenser lens 3103, and the mask 100 is illuminated by the condenserlens 3106. The light having transmitted through the mask is partlyshielded by an imaging spatial filter 3302 and imaged on the wafer 200by an imaging lens 3201. Let 1 (u, v) be the shape of the light sourcespatial filter 3301, f (x, y) be the shape of a pattern on the mask 100and a (u, v) be the shape of the imaging spatial filter 3302, then theintensity gp (x, y) of an image on the wafer 200 is calculated by anexpression (1) below: ##EQU1##

In the expression (1), the intensity at the imaging surface isintegrated after calculation since lights exited from (u, v) on thelight source spatial filter 3103 are not interfered with each other.According to "Vibration Optics" (Iwanami Shoten) written by Kubota,generally, a resolving power of an optical system can be consideredusing a response function or OTF (Optical Transfer Function) of theoptical system. A response function (u, v) in the example shown in FIG.4 is calculated by the following expression (2) using a pattern f (x, y)on an object surface and the strength gp (x, y) of an image thereof.##EQU2##

FIG. 8 shows the response function of the optical system calculated fora curve 351. The abscissa indicates the spatial frequency s, and showsthe number of openings (in case of NA=0.38) of the corresponding imaginglens for reference. The ordinate indicates the response functionnormalized by the O-order component. The position of point 355 indicatesthe size of an opening of the imaging lens. The curve 352 indicates theresponse function in the case where conventional optical systems, i.e.the light source spatial filter 3301 and the imaging spatial filter 3302are not used; the curve 353 indicates the apparent response function byway of the phase shift method; and the curve 354 indicates the responsefunction in the case where coherent light such as laser is used forreference. In the response function 352 according to the conventionalmethod, the response function extends to a position S1 indicated by thefollowing expression (3): ##EQU3##

The method of the present invention is the same as the conventionalmethod in that the response function extends to the position shown inthe above-described expression (3) but the curve is in the shapestabilized to the position of 0.6 from a portion near N.A.=0.2.Furthermore, in the present invention, the response function of a lowfrequency component is lowered by devising the shape of the mask patternas described later so that the response function of the whole systemaccording to the present invention has a shape of curve 356. A curve 357is shown normalized, and a stabilized response function extends over awide zone from the low frequency component to the high frequencycomponent. Thereby, a fine pattern can be imaged with high contrastaccording to the present invention. More specifically, for example, aline and space of 3 μm is at a position of point 358, and this contrastis C1 in the conventional method whereas it will be a high value, C2, inthe present invention. In the present invention, shapes of the lightsource filter 3301 and the imaging spatial filter 3302 are determined soas to optimize the response function calculated by the aforesaidexpression (1). According to the present invention, the value of theresponse function of the high frequency component can be relativelyincreased by decreasing the response function of the low frequencycomponent. In addition, a ring-like light source spatial filter can beused to extend the response function to the area set by the expression(3).

The size and width of the light source spatial filter 301 and imagingspatial filter 3302 can be optimized by calculating the responsefunction using the aforesaid expression (2).

The method for calculating the imaging state at the wafer 200 bysimulation to confirm the shape of a mask will be described later butthe expression (1) cannot be analytically solved, and numericalcalculation based on the expression (1) is used for calculation. Whenthe response function capable of being calculated by the expression (2)is obtained and calculated by the expression (4) below, calculation timecan be shortened.

    gp(x, y)=| [H(u, v)* [f(x, y)]]|.sup.2   (4)

A method for determining shapes of a light source spatial filter 3301and an imaging spatial filter 3302 is shown in FIGS. 9 to 14. An opticalsystem of the present invention is an optical system of so-calledpartial coherent imaging. An optical system of partial coherent imagingthat cannot be fully explained using a so-called response function isexplained in "Stepper's Optics" (Optical Technical Contact, Vol. 27, No.12, pp. 762-771). The imaging characteristics of the optical systemusing a ring-like light source and a ring-like spatial filter accordingto the present invention on the basis of the aforementioned concept arecalculated.

The imaging characteristic of the partial coherence imaging iscalculated by expression (5) below using the concept of TransmissionCross-Coefficient, T(X₁, X₂) showing the relationship between a shape ofa light source and a shape of the pupil surface of a detection opticalsystem. According to the aforementioned "Stepper's Optics", OTF (OpticalTransfer Function) of the optical system is approximately determined byTransmission Cross-Coefficient, T(x, O) of the minimum order. T(x, O) isshown by the relative function between the shape of the light source andthe shape of the pupil surface.

    gp(v)=∫∫T(X.sub.1, X.sub.2)ƒ(X.sub.1)ƒ*(X.sub.2) exp [-2 πi v·(X.sub.1 -X.sub.2)]dX.sub.1 dX.sub.2

where

v=(x, y) . . . Coordinates on image surface

x₁ =(u₁, v₁) Coordinates on pupil (u₂, v₂) surface

f(x₁) . . . Intensity distribution on image surface

. . . Fourier conversion

* . . . Conjugate complex number

    T(X.sub.1, X.sub.2)=∫l(X.sub.3)a(X.sub.1 +X.sub.3)a*(X.sub.2 +X.sub.3)dX.sub.3                                         (5)

That is, the characteristic of the partial coherent imaging shown by thecomplicated expression (5) poses a problem of geometry which is therelative function between the shape of the optical source and the shapeof the pupil surface. FIG. 9 shows a light transmission portion 3305 ofa light source spatial filter 3301 and a light shield portion 3306 of animaging spatial filter 3302. The relative function between the lightsource and the pupil surface with coordinates x is shown by an area ofan oblique line portion or hatched portion 364 in FIG. 9. Similarly, therelative function between the light source and the pupil surface in theprior art is shown by an oblique line portion or hatched portion in FIG.10.

A curve 367 in FIG. 13 shows a calculated value of the relative functionin the case of FIG. 9, in other words, Transmission Cross-Coefficient,T(x, O). The relative function in case of the prior art shown in FIG. 10is large in value in a high frequency area as compared with the curve366. That is, the contrast increases. FIG. 13 shows the calculatedresult in case of N.A.=0.38, σ=0.9. In FIG. 13, an abscissa shows theminimum pattern dimension corresponding to each N.A. in the case wherewavelength is 0.365 micron. (For example, 0.3 means line and space of0.3 micron.) It is understood that OTF of 0.3 micron is about twice aslarge as that of the prior art.

FIGS. 12 and 13 are views for increasing the intuitive understanding ofand helping the setting of shapes of the light source spatial filter3301 and the imaging spatial filter 3302. A hatched portion A in FIG.11(a) shows the relative function between the outer diameter of thelight source and the shield portion 3306, and a hatched portion B inFIG. 11(b) shows the relative function between the inner diameter of thelight source and the shield portion 3306. A hatched portion C in FIG.11(c) shows the relative function between the transmission portion 3305of the light source and the maximum pupil of the optical system. Therelative function between the final light-source shape and the spatialfilter is shown by the hatched portion 367 in FIG. 12. This can beobtained by C-A+B. By obtaining the relative functions as describedabove, the effect of the spatial filter or ring-like illumination can beintuitively understood, and conversely, that is helpful in determiningthe shape thereof. More specifically, the value of the high frequencyarea 382 is larger in value than the intermediate frequency area 381. Inthe case where the value of the low frequency area 383 is excessivelylarge, the value of the low frequency area is further reduced from theeffects A and B of the spatial filter. In this way, the effect of thering-like illumination and the spatial filter is intuitively explained.

Of course, the shape of the light source and the shape of the spatialfilter should be evaluated on the basis of expression (5) and should beapproximately evaluated by the relative function between the lightsource and the spatial filter.

Since the ring-like light source can make the coherence high, the depthof the optical system can be increased. The narrower the band width ofthe ring-like power source the higher the coherence of the light source.Thus, the focal depth increases. The larger the diameter of the ring ofthe ring-like light source the greater the coherence degree of space.Thus, the resolution increases.

The effects of the ring-like light source and ring-like spatial filterused in the present invention will be described with reference to FIG.15. FIG. 15(a) shows an eye 3301 of an imaging lens, an image 3305a (theO-order diffraction light) of a light source imaged on the eye, anddiffraction images 3305b and 3305c of a light source resulting from apattern (a circuit pattern) formed in a direction of y on a mask 100.FIG. 15(a) shows the case where the light source is ring-like, and FIG.15(b) shows the case where the light source is circular. A filter forshielding the O-order diffraction light is shown by an hatched portion371. A cross-hatched portion 372 which is also a part of the diffractionlight 3305b and 3305c of the light source is simultaneously shielded bythe oblique line 37. In case of FIG. 15(a), only 10% to 20% areshielded, but in case of FIG. 15(b), 40% or more are shielded. That is,the object for efficiently shielding only the O-order diffraction lightis effectively achieved by the ring-like light source of FIG. 15(a).Namely, the ring-like light source is improved in performance. Thesmaller the width of the ring-like light source, the smaller the ratioof the diffraction light to be shielded becomes.

In the present invention, a spatial filter 3306 having a ring width ofnarrowness about 30% of the ring width of the light source as shown inFIG. 16(a) is used in order to shield a part of the O-order diffractionlight. However, since a part of the O-order diffraction light willsuffice to be shielded, a spatial filter as shown in FIG. 40(b) can beused in which the ring width is substantially the same as the lightsource and the transmittance is approximately 70%. Of course, the ringwidth can be made smaller than that of the image of the light source andthe transmittance can be lowered than 70%. Furthermore, while here, thecase where the light transmittance is 30% or less, it is to be notedthat the light transmittance is not limited to 30%. It is to be furthernoted that as a spatial filter portion 3306, use can be made of a phaseplate in which the transmittance is 100% and a phase at the usingwavelength is deviated by π in order to shield a part of the O-orderdiffraction light. Such a filter may serve as a filter for substantiallyshielding a part of the O-order diffraction light. Furthermore,polarized light and a polarizing plate may be used for shielding.

Further, as shown in FIG. 26, the ring width of the filter in whichtransmittance is 70% may be made larger than that of the light source.With this structure, not only the O-order diffraction light, but also apart of the low-order diffraction light can be shielded, and an MTFcurve can be improved. Also in an example shown in FIG. 16(a), astructure is shown in which a part of the low-order diffraction light isshielded as in the example of FIG. 26.

As described above, in order to efficiently shield the O-orderdiffraction light, the ring-like light source exhibits the effect. Whenthe width of the ring is made small, the effect increases. It can behere considered that a ring-like light source comprises light sourcesaligned in a ring-like fashion. That is, it can be considered as anassembly of coherent point sources. Thus, the object of the presentinvention is achieved even by the provision of an assembly of lightsources 375 having a spatial coherence in the order of 0.1 to 0.3 closeto point sources and shield plates 376 smaller than the light sources375 positioned corresponding thereto. Needless to say, the shield plate376 of low transmittance may be used. FIG. 17(a) shows an example inwhich the light sources 375 and the shield plates 376 are aligned in aring-like fashion. When this type of arrangement is employed, theshielding of the O-order diffraction light is achieved even if thering-like shape is not formed, as shown in FIG. 17(b). At the same time,several plies of light sources and shield plates can be aligned as aring, as shown in FIG. 17(c). A shield plate may be mounted with respectto only a part of the corresponding light source in order to shield apart of the O-order diffraction light as shown in FIG. 17(d).

FIGS. 18(a) and 18(b) show the distribution of light intensities of alight source and the transmittance of a spatial filter in connectionwith the radius direction. While in FIG. 18, both the light intensitydistribution and transmittance distribution are shown in the rectangulardistribution, it is to be noted that a gentle distribution as shown inFIG. 19(a) and 19(b) may be employed without problem. This can beunderstood if one considers that OTF is shown by their relativefunctions. That is, since an integrated one while taking weighting isthe relative function with respect to duplicated portions, even if thegentle distribution is exhibited, the value of the relative functiondoes not change greatly. In any case, radially equal distributions andconcentrical distributions are obtained, which are important. The factthat the light source described herein may have the distribution asshown in FIG. 19(a) indicates that the intensities of the light sourcesshown in FIGS. 17(b), (c) and (d) become small toward the center. Insuch an embodiment, there are effects in that a light source with lesscoherency can be prepared and at the same time a frequency component canbe further made small.

As described above, in the present invention, the effective shielding ofa part of the O-order diffraction light by the exposure apparatus orother imaging optical systems enabling the enhancing of the resolutionand enhancing of the focal depth. However, in order to efficientlyshield the O-order diffraction light, it is necessary not to superposethe O-order diffraction light and the diffraction light on a Fouriertransform surface in which a spatial filter is arranged, but where theyare separated. To this end, the coherency of the illuminated lightshould be high. That is, it is desirable to be close to a point source.On the other hand, in order to enhance the resolution of the imagingoptical system, it is desirable to increase the spatial, coherence ofthe light source, namely, the α value. That is, a large light source isdesired. As a contradiction to each other (a point source and a largelight source) need be compatible. The ring-like light source and thespatial filter according to the present invention makes suchcontradiction as noted above compatible. One way of efficientlyfulfilling this is to use an assembly of small light sources. Further,if this assembly is arranged in the form of a large ring, the conditionof a large light source is fulfilled. That is, if the width of the ringis made small, the coherency increases and the focal depth enhances,whereas if the radius of the ring is made large, the spatial coherencyincreases and the resolution enhances.

There is present a condition that when the radius of the ring increaseswhile shielding a part of the O-order diffraction light, the diameter ofthe spatial filter 3306 becomes about the same as that of the eye of theoptical system. This condition is a condition that a part of the O-orderdiffraction light is shielded and the size of the ring-like light sourceis maximum. That is, this is a condition that the maximum resolution isobtained in connection with the reduction projection lens. FIGS. 20(a),(b) and (c) show such arrangement. In these embodiments, the size of thelight source is larger than the lens eye. Generally, it has been saidthat when the size of a light source is increased, the focal depthbecomes shallow, and cannot be properly used for lithography. However,as already explained above, a ring-like light source can be used tothereby make the focal depth deep. Therefore, it is possible to use alight source larger than an eye as shown in FIG. 20. The individualembodiments have a structure in which a part 377 of the O-orderdiffraction light is shielded. The OTF of this structure is indicated bythe relative function. Therefore, there is an effect that the shut-offfrequency of the OTF is extended in comparison to the case where thesize of a light source is smaller than an eye. Furthermore, a furthereffect obtained by this structure lies in that the resolution can beenhanced only by an improvement in an illuminating system whichfacilitates a large N.A. implementation without using a reductionprojection lens which requires high precision. In this embodiment, it ispossible to transfer a pattern of approximately 0.2 μm with a wire iusing a lens of N.A. 0.4.

It is important for an imaging system of the O-order diffraction lightshield to gently and monotonously reduce an OTF curve. FIG. 21 shows anOTF curve 378 according to the present invention. In the case where theOTF is not a gentle or smooth curve, but rather is wavy as shown bycurve 379, the contrast in the vicinity of an extremely small point ofthe wave lowers, and in an actual LSI pattern having various spatialfrequency components, the pattern is not properly transferred. However,a special pattern formed from only specific spatial frequency componentsis not included herein, and the contrast will suffice to be increasedwith respect to the specific spatial frequency. That is, the OTF curveneed be in the range of the specific width Wb as shown in FIG. 22. ThisWb should be calculated from the transfer result calculated by atransfer simulator later described.

Accordingly, also in the case where a light source shown in FIG. 20 islarge, the OTF which gently and monotonously reduces is required. It isdesired from this that when a pattern of actual LSI is transferred, adifference between an inner diameter of a light source and a diameter ofan eye of a reduction projection lens is substantially equal to adifference between an outer diameter of a light source and a diameter ofan eye of a reduction projection lens. In order to obtain an actualfocal depth, it is desired that the ratio between the eye diameter ofthe reduction projection lens and the inner diameter is 0.6 or more.

In the example of FIG. 20(a), a filter having a transmittance of asuitable value may be arranged at a portion of a portion 380, as shownin FIG. 25, exposed to the O-order diffraction light of the light sourcewithin the eye of the reduction projection lens. In this case, it ispossible to reduce the width of a portion 377 externally of the eye ofthe light source, and thus, there is also an effect that the size of thelight source can be reduced.

Conversely, it is possible to increase the width of a portion 380 in theeye of the reduction projection lens as compared with portion 377. Thisbrings forth effects such that a stabilized contrast is easilymaintained in a wide area where the light intensity is easily increased.

Furthermore, even if the outer diameter of the light source of the ringis made to be the same as that of the eye of the reduction projectionlens, the object of the present invention can be achieved to someextent. In the structure shown in FIG. 20(a), a spatial filter is notintroduced into the eye of the reduction projection lens so that a partof the O-order diffraction light can be cut. Therefore, the structure issimple and the operation can be easily performed.

Moreover, as shown in FIG. 23, a ring-like light source 378 is installedexternally of the light source shown in FIG. 20 to further enhance theresolution. FIG. 24 shows an example in which the light source shown inFIG. 23 is embodied. Since the light source with N.A. increased asdescribed above is difficult in the lens system, a laser light source3121, a beam scanning means 3122, ring-like mirrors 3123 and 3124 areused. In the case of this embodiment, a lens of N.A. 0.4 of i wire isused, and 0.15 μm can be resolved. Such embodiment does not differ fromthe fundamental idea of the present invention in that a part of theO-order diffraction light is shielded.

One embodiment of a pattern transfer system 3000 (a reduction projectionexposure optical system) according to the present invention will bedescribed hereinbelow with reference to FIGS. 4 to 6. In the patterntransfer system (reduction projection exposure optical system) 3000, ani-ray having a wavelength of 365 nm out of light from a Hg lamp 3101 isselectively transmitted by a color filter 3102, and the light iscondensed on the surface of an integrator 3104 by a condenser lens 3103.Light incident upon elements 3107 (FIG. 28) in the integrator 3104 areindividually emitted with an angle of exit α, and a mask 100 isilluminated by a condenser lens 3106. The integrator 3104 will bedescribed later. A ring-like light source spatial filter 3301 isinstalled in the vicinity of an output end of the integrator 3104.

The light having transmitted through a mask circuit pattern 104 (shown,for example, in FIG. 39) on the mask 100 and diffracted is imaged andtransferred as a wafer circuit pattern 204 (shown, for example, in FIG.37) having a high contrast on the wafer (substrate) 200 through animaging lens (reduction projection lens) 3201 and an imaging spatialfilter 3302 mounted in the vicinity of a pupil of the imaging lens.

It is noted that an image of a light source spatial filter 3301 in theform of a ring is imaged at a position of an imaging spatial filter 3302in the form of a ring by the condenser lens 3106 and the imaging lens(reduction projection lens) 3201. The imaging relationship between thelight source spatial filter 3301 and the imaging spatial filter 3302 inthe present embodiment is shown in FIGS. 32 and 33. The light sourcespatial filter 3301 forms a light source of a ring portion 3305 havingan outside diameter DLO and an inside diameter DLI, and both inside andoutside of the ring portion 3305 are shielded. The imaging spatialfilter 3302 has a construction in which a ring portion 3306 having anoutside diameter DIO and an inside diameter DII is shielded, and lighttransmits through both inside and outside of the ring portion 3306. Anincident portion of the imaging lens (reduction projection lens) 3201 isindicated at 3205 and an exit portion is indicated at 3206.

The imaging spatial filter 3302 may be at a position 3202 in front 3205of the imaging lens (reduction projection lens) 3201, at a position 3204at the rear 3206 of the imaging lens 3201 or at a position 3203 of apupil in the imaging lens. The best effect in design is obtained at theposition 3203, and a position at which cost is minimum and sufficienteffect is obtained is the position 3204.

FIG. 11 is a perspective view of the imaging lens 3201 in which theimaging spatial filter 3302 is arranged at the position 3204. In thiscase, the imaging spatial filter 3302 is formed from a metal plate andtherefore supported by support rods 3311. Needless to say, the smallerin number and smaller in diameter of the support rods 3311, the better.FIG. 31 shows an embodiment of the imaging spatial filter 3302 formed infront of or at the rear of the imaging lens 3201 by forming a shieldfilm 3313 on a glass substrate 3312. In this case, the support rod isnot necessary but the imaging lens 3201 need be designed inconsideration of aberration caused by the glass substrate 3312.

Let M be the imaging magnification between the light source spatialfilter 3301 and the imaging spatial filter 3302, the relationshipbetween DLO which is an outside diameter of the light source spatialfilter 3301, DLI which is an inside diameter of the light source spatialfilter 3301, DIO which is an outside diameter of the imaging spatialfilter 3302 and DII which is an inside diameter of the imaging spatialfilter 3302 as shown in FIG. 32 will be described later. In short, if apart or the whole of the O-order diffraction light is shielded, a finecircuit pattern on a mask can be imaged on a wafer with high contrast.

As described above, with respect to DIO and DII of the imaging spatialfilter 3302 as well as DLO and DLI of the light source spatial filter3301, a variable spatial filter such as a liquid crystal display elementis constituted or a plurality of spatial filters which are different indimension from one another are exchangeably provided whereby thering-like dimension of the spatial filters can be controlled.

One embodiment of the entirety of a projection exposure system accordingto the present invention will be described hereinafter with reference toFIGS. 27 to 36.

First, a pattern data producing system 1000 as shown in FIG. 27 will bedescribed. In the pattern data producing system 1000 and in a wiringdata preparing portion 1102, wafer pattern shape data 1103 desirablyformed on a substrate (wafer) 200 is formed on the basis of a wiringdrawing data 1101 such as design data. A pattern conversion portion 1104converts a mask pattern shape data 1105 desirably formed on a mask(reticle) 100 on the basis of the wafer pattern shape data 1103. At thattime, a pattern transfer simulator 1108 checks whether or not a maskpattern on the mask converted by the pattern conversion portion 1104approximately coincides with the wafer pattern shape data 1103 whenactually exposed on the substrate 200 by a pattern transfer opticalsystem on the basis of the wafer pattern shape data 1103 formed by thewiring data preparation portion, the setting conditions such as theoutside diameter DLO, the inside diameter DII or the like of a ringportion 3305 of a light source spatial filter 3301 and the settingconditions of the outside diameter DIO, the inside diameter DLI or thelike of a ring portion 3306 of an imaging spatial filter 3302. The maskpattern is then fed back to the pattern conversion portion 1104 forcorrection to obtain an optimum shape (such as the outside diameter DLO,the inside diameter DLI or the like of the ring portion 3305, and theoutside diameter DIO, the inside diameter DII or the like of the ringportion 3306) of the spatial filter adjusted to the wafer pattern shapedata 1103, results of which are sent to a light source spatial filtercontrol portion (an adjusting portion) 3303 and an imaging spatialfilter control portion (adjusting portion) 3304 through a spatial filtercontrol system 3305 to control (adjust) the shape of the light sourcespatial filter 3301 and imaging spatial filter 3302. The patternproducing portion 1106 converts an EB data 1107 suited to an electronbeam depicting device 2103 on the basis of the mask pattern shape data1105 converted by the pattern conversion portion 1104.

Next, a mask fabrication system 2000 will be described. A film formingdevice 2101 forms a plurality of stacked films 202 formed of metalchrome or chrome oxide or metal chrome and chrome oxide on a masksubstrate 101. A coating device 2101 coats a resist film 203 on the masksubstrate 101 formed by the film forming device 2101. The electron beamdepicting device 2103 depicts and forms the same circuit pattern as themask pattern shape 1105 in accordance with the EB data 1107 producedfrom the pattern producing portion 106. Thereafter, a circuit pattern onthe mask substrate 201 is developed by a developing device 2104 tocomplete a mask 100. The completed mask 100 is inspected in pattern bycomparing image data detected by a pattern inspection device 2106 withmask pattern data 1103 or wafer pattern data 1105 or data from thetransfer simulator 1108. If a defect is present, it is corrected by apattern correction device 2105 composed of an ion beam machine or thelike, and finally, a foreign particle on the mask 100 is inspected by aforeign particle inspection device 2107. If a foreign particle ispresent, it is washed by a washing device 2108. The mask 100 accordingto the present invention is characterized in that it is easily washed ascompared with a mask of a phase shifter since the mask can be formed ofa single layer film 102 as shown in FIG. 39, for example. Furthermore,the mask 100 can be easily manufactured as compared with a mask of thephase shifter. In the pattern inspection device 2105, the detected imagedata may be compared with any of the mask pattern data 1103 or the waferpattern data 1105 or data from the transfer simulator 1108. However,most effectively, the light source of the pattern inspection device 2105and the forming optical system is made equivalent to a pattern transfersystem (reduction projection exposure system) 3000 according to thepresent invention to compare it with the wafer pattern data 1105. Morespecifically, the pattern inspection device 2105 is composed of anoptical system equivalent to the pattern transfer system (reductionprojection exposure system) 3000, and a mask 100 to be inspected isplaced on a mask stage 3401 and a light receiving element is arranged ata position in which a wafer (substrate) 200 is placed so as to detect animage to be imaged on the light receiving element. With the patterninspection device 2105 designed as described above, the same circuitpattern as an extremely fine circuit pattern actually projected andexposed to the wafer (an extremely fine circuit pattern of 1 μm or lesson a wafer) can be detected as an image signal with high contrast fromthe light receiving element without being effected by interference oflight, and as the result, it is compared with the wafer pattern data1105 whereby even a fine circuit pattern can be inspected accurately.

Next, a pattern transfer system (reduction projection exposure opticalsystem) 3000 of the present invention will be described hereinafter. Inthe pattern transfer system 3000, an i-ray having a wavelength of 365 nmout of light from a Hg lamp 3101 is selectively transmitted by a colorfilter 3102 and condensed on the surface of an integrator 3104 by acondenser lens 3103. Light incident on elements 3107 (FIG. 28) in theintegrator 3104 individually exit at an angle of exit to illuminate theupper portion of the mask 100 by a condenser lens 3106. FIGS. 28 and 29show different modes of the integrator 3104. FIG. 28 shows the casewhere a section of the integrator 3104 is in the form of a ring. FIG. 29shows an embodiment of the integrator 3104 in which a ring-like shape isformed by a shield plate 3105. In short, it is obvious that otherconfigurations may be employed as long as one performs a role of aspatial filter, that is, a ring has a shield function. Preferably, theDLI and DLO of the light source spatial filter 3301 configured asdescribed above can be controlled by the provision of a plurality ofspatial filters different in dimension from one another so that they areexchanged whereby they can be controlled or adjusted by a command from alight source spatial filter control portion (adjusting portion) 3303.Otherwise, a freedom is greatly restricted.

In the present invention, when a shield plate is placed on a lightsource surface, a synthetic light quantity is reduced. Accordingly, itis necessary to increase the light intensity of the light source. In aconventional lamp, it has been difficult to increase the lightintensity. The strobe light source for fiber illumination is disclosedin "Development and Research of Strobe Light Source for FiberIllumination" written by Yamamoto, Lecture Meeting of Society of AppliedPhysics, 1991, 11p-ZH-8-. The strobe light source as disclosed thereinhas not been used for an exposure apparatus. However, it is effectivefor the present invention which requires to sufficiently obtain thelight intensity to use a lamp as described. This light source is suitedto the present invention because it has a larger diameter.

In the embodiment shown in FIG. 23, an integrator using an optical fiberas shown in FIG. 25 is effective. The integrator using an optical fibercomprises a bundle of a number of optical fibers 380. A lightintroducing surface 3131 is circular in shape so as to easily condenselight from a light source 3101, and a light emitting surface comprises abundle of optical fibers so as to be a ring-like configuration. By usingthe optical fibers, a light source having a circular light source shapesuch as a mercury lamp can be used to efficiently prepare a ring-likelight source. An integrator 3104 can be prepared to be flexible by usingthe optical fibers. This brings fourth an effect in that a light sourceas a hearing source can be installed at a position away from theapparatus body which requires temperature control.

It is suggested that a bundle of fibers shown in FIG. 25 is scattered sothat the outer and inner diameters can be varied. Such a variablemechanism is controlled by a light source spatial filter controlmechanism 3303.

Light having transmitted through a mask pattern 104 (FIG. 34) on a mask100 and diffracted is imaged as a wafer pattern 204 (shown, for example,in FIG. 37) on a wafer 200 through an imaging lens 3201 and an imagingspatial filter 3302.

The imaging spatial filter 3302 may be at a position 3202 in front ofthe imaging lens 3201 or at a position 3204 at the rear of the imaginglens or at a position 3203 of a pupil in the imaging lens.

An image of the light source spatial filter 3301 is imaged at a positionof the imaging spatial filter 3302 by the condenser lens 3106 and theimaging lens 3201. FIGS. 32 and 33 show the imaging relationship betweenthe light source spatial filter 3301 and the imaging spatial filter 3302in the present embodiment. The light source spatial filter as well asthe imaging spatial filter have a shape of a ring. The light sourcespatial filter 3301 has a ring portion 3305 having the outside diameterDLO and the inside diameter DLI, and both the inside and outside of thering portion 3305 are shielded. In the imaging spatial filter 3302, thering portion 3306 having the outside diameter DIO and inside diameterDII is shielded, and it is designed so that light transmits through boththe inside and outside of the ring portion 3306. Let M be the imagingmagnification between the light source spatial filter 3301 and theimaging spatial filter 3302, the relationship of the followingexpression (6) is established between DLO, DLI, DIO and DII:

    DIO=M·δ·DLO

    DII=M·ε·DLI

    M·DLI≦DII≦DIO≦M·DLO (6)

wherein d and d are the coefficients, which are fulfilled with thefollowing expression (7):

    0.7≦δ≦1.0

    1.0≦ε≦1.3                            (7)

When these coefficients are fulfilled with the above-describedexpression (7), the effect of the present invention is most conspicuous.However, these expressions need not always be satisfied but a part orthe whole of the O-order diffraction light may be shielded. In setting δand ε, values of δ and ε of the spatial filter with highest contrast areselected by the pattern transfer simulator 1108.

FIG. 42 shows the contrast when the values of δ and ε are changed. Inthis figure, when δ is 0.8 and ε is 1.1, the best contrast is obtained.However, it is apparent from FIG. 3 that the best contrast is notobtained only at the time of the aforesaid values.

Let NAO be the number of openings of the imaging lens (reductionprojection optical system) 3200 on the exit side 3204, and NAL be thenumber of openings of one in which a light source image is projected atthe same position 3204. The NAL/NAO is defined as a spatial coherencedegree σ. FIG. 43 shows the relationship between σ and the contrast.When σ is about 0.9, the best contrast is obtained. However, even if σis somewhat deviated from 0.9, high contrast is obtained.

The object of the present invention is achieved most conspicuously inthe case where a light source spatial filter 3301 and an imaging spatialfilter 3302 shown in FIG. 13 are used. However, since the object of thepresent invention is achieved by shielding a part of the entirety of theO-order diffraction light, even if an air filter shown in FIGS. 14 to 17is used, a circuit pattern with high contrast can be imaged on a wafer.In the air filter shown in FIGS. 14 to 17, an oblique line shown thereincomprises a shield portion. A pattern transfer system 3000 comprises alight source portion 3100 comprising a Hg lamp 3101, a color filter3102, a condenser lens 3103, an integrator 3104 and a condenser lens3106; an imaging optical system 3200 comprising an imaging lens 3201; aspatial filter control system (a regulating system) 3300 comprising anentirety control portion 3305 for delivering control signals to a lightsource spatial filter control portion (regulating portion) 3303, animaging spatial filter control portion (regulating portion) 3304 and alocating mark detection portion 3403 on the basis of command signalssuch as DLO, DLI, DIO, DII, etc. obtained from a light source spatialfilter control portion (regulating portion) 3303 for controlling a lightsource spatial filter 3301, an imaging spatial filter 3302 and a lightsource spatial filter 3301, an imaging spatial filter control portion(regulating portion) for controlling an imaging spatial filter 3302 anda pattern transfer simulator 1108 to control the entirety; and alocating portion 3400 comprising a mask stage 3401 placing thereon amask 100, a wafer stage 3402 placing thereon a wafer 200, a locatingmark detection portion 3403 for detecting a locating mark on the wafer,a mask stage control system 3404 for controlling a mask stage 3304 inaccordance with a command from the locating mark detection portion 3403and a wafer stage control system 3405 for controlling the wafer stage3402 in accordance with a command from the locating mark detectionportion 3403.

With the above-described arrangement, the operation is as follows: Amask 100 fabricated by a mask fabrication system 2000 is placed on themask stage 3401 and illuminated by the light source portion 3100. A partof the O-order diffraction light having transmitted from the mask andfrom the light source spatial filter 3301 in the light source portion3100 is shielded by the imaging spatial filter 3302, and high orderdiffraction light and part of the O-order diffraction light pass throughthe imaging optical system (reduction projection lens) 3200 to form acircuit pattern on the wafer 200.

A ring-like spatial filter as shown in FIG. 32 is used as the spatialfilter because a coherence is provided on the light source. Thecoherence has two types, one for time, and the other for space. The timecoherence is a wavelength band of the light source, the shorter band oflight, the higher the coherence. The spatial coherence is the magnitudeof the light source, which corresponds to the magnitude of the lightsource spatial filter 3301. However, when the magnitude of the lightsource is made small in order to increase the coherence, the lightintensity of the light source becomes small and the exposure timebecomes extended, as a consequence of which through-put of the exposurefalls. When the ring-like light source spatial filter 3301 is used, animage of the light source spatial filter 3301 formed at the imagingposition is the O-order diffraction light. That is, the use of thering-like spatial filter 3301 can realize a light source which is highin intensity and has a coherence. This is the same art as that uses aring-like spatial filter to obtain a coherent light from a white lightin a phase difference microscope, which is disclosed in "Wave Optics"(Iwanami Shoten) written by Kubota.

There is a further reason why the light source spatial filter 3301 has aring-like shape. As previously explained, there is a relationship, asshown, between a dimension of a pattern on a wafer desired to betransferred and a spatial coherence degree of a light source by which apattern with that dimension is transferred with highest contrast. Thus,when the space coherence degree adjusted to a dimension (pitch) of apattern desired to be transferred, the effect of the present inventionconspicuously appears. If the light source spatial filter 3301 and theimaging spatial filter 3302 are formed on the ring, the spatialcoherence degree, i.e., the size of the ring is easily controlled.

However, needless to say, the ring radius (spatial coherence degree) ofthe ring-like light source and space filter is made as large as possibleto enhance the resolution.

In the present invention, the ring-like light source as well as thespace filter are of a concentric circle. By the provision of aconcentric circle, a directivity with respect to a circuit pattern to betransferred by MTF cannot be provided. In transferring an LSI circuitpattern having circuit patterns of various directions, it is importantthat MTF has no directivity. The concentric filter has an effect thatcomplicated aberrations are hard to enter a lens as compared with anon-concentric filter as shown in FIG. 36.

Since the aforesaid effect can be achieved if the intensities of theO-order diffraction light and the high order diffraction light arebalanced, the effect though somewhat low can be achieved even when theimaging spatial filter 3302 is omitted and only the light source filter3301 is provided. Conversely, even the light source spatial filter 3301is omitted and only the imaging spatial filter 3302 is provided, theaforesaid effect though somewhat low can be achieved.

Next, a method for forming a pattern will be described in more detailwith reference to FIGS. 37 to 41. As described above, the object of thepresent invention can be achieved by using the light source spatialfilter 3301 and the imaging spatial filter 3302 but the effect of thepresent invention can be further enhanced by devising a mask pattern 104as will be described below.

FIG. 45 shows an imaging optical system 3200 with a line width (lighttransmission) of a line spatial pattern having the same pitch formed ona mask 100 changed and a contrast of a circuit pattern projected on awafer 200. As shown in FIG. 44, contrast becomes large as the line widthbecomes small. That is, the line width is suggested to make small. Whenthe line width is made small, the light intensity is small, andtherefore, it is necessary to extend the exposure time. The line widthof the circuit pattern formed on the mask 100 is determined inconsideration of the contrast and exposure time required to transfer acircuit pattern.

Accordingly, preferably, in the exposure method according to the presentinvention, the line width for forming the mask pattern 104 is madeconstant. For this reason, in the case where a wide wafer pattern 204 isdesired to be formed, a device is required. In the case where the linewidth is not constant but wide, the light intensity at the imagingsurface is high with respect to a pattern in which a peripheral linewidth is constant, and a shape of a transferred pattern after resistdevelopment is far apart from a circuit pattern to be obtainedoriginally. In the case where there is partly a circuit pattern whoselight intensity is high, this results from light which comes therefrom.

To properly form a wide circuit pattern, it is necessary to form thelight intensity with the same light intensity as the circuit patternwhose peripheral line width is constant. The method for forming a widecircuit pattern will be described with reference to the figure. When acircuit pattern is transferred by use of the imaging optical system3200, a circuit pattern which is sufficiently small than a resolvingpower of the imaging optical system cannot be resolved but imagedevenly. In imaging the aforesaid wide circuit pattern, this phenomenonis utilized. That is, when a fine pattern less than a resolving power ofthe present optical system is formed on a mask 100 as indicated at 105,106 and 108 in FIGS. 39 and 40, a wide circuit pattern can betransferred to a wafer 200 as shown in FIGS. 37 and 38.

FIG. 45 shows a contrast when the pitch of a line space pattern changed.As shown in FIG. 45, as the pitch becomes small, the contrast becomessmall. That is, when the pitch is made small, there is a position 331 atwhich the contrast is approximately 0. In the case where the wholesurface of the wide circuit pattern is desired to be white, a patternhaving the pitch at that position 331 may be used. More specifically,most preferably, there is used a pattern having a pitch approximately1/2 of a pitch of a pattern to be resolved. At this pitch, the lightintensity of the wide circuit pattern is about the same as that of theminimum pattern.

More specifically, in the case where a wafer pattern 204 as shown inFIG. 37 is to be obtained, a mask pattern as shown in FIG. 39 isfabricated, and a negative resist is used, or a mask pattern as shown inFIG. 40 is fabricated and a positive resist is used. In this case,patterns 105, 106, 107 and 108 desired to transmit light therethroughare formed by patterns having a small pitch as shown in FIG. 41. A maskpattern 104 in the case where light is transmitted over a wide range asin these patterns 105, 106, 107 and 108 is automatically produced by apattern conversion portion 1104 and is simulated by a pattern transfersimulator 1108 as needed.

A pattern of 1/2 pitch may be 1/2 pitch in only one of X-direction andY-direction. Needless to say, of course, a grating pattern which has 1/2pitch in both X- and Y directions is employed. The pitch need not alwaysbe 1/2 but other pitches may be employed at which the light intensity onthe wafer pattern 204 is sufficient as needed.

Even in the case of a mask in which an extremely fine circuit patternand a large circuit pattern are mixed, the transfer can be made by onereduction projection exposure by the aforementioned method. However, inthe case where an extremely fine circuit pattern and a large circuitpattern are transferred by more than twice reduction projectionexposure, the aforementioned method need not be employed but a pattern104 can be formed merely by a pattern whose line width is constant. Inthis case, there is an effect in that a system such as the patternconversion portion 1104 is not necessary.

As described above, the method of the present invention has an effect inthat since a phase shifter need not be arranged, processing by thepattern conversion portion 1104 is simple, and time can be saved and anerror can be reduced.

While in the present embodiment, a mask pattern has been converted witha circuit pattern having a constant line width as a base, it is to benoted that in a circuit pattern which involves many repetitive portionssuch as memory, a mask pattern 104 so as to obtain an optimum waferpattern 204 while being simulated by a transfer simulator 1108 can beobtained. Namely, the mask pattern 104 is obtained by the transfersimulator 1108 for every memory cell.

A transfer mechanism on a wafer of a mask pattern will be describedreferring again to FIGS. 1, 2 and 3 wherein FIG. 1(a) is a sectionalview of a mask 100 in which a mask pattern 104 is formed of chrome 102on a glass substrate 101. A waveform 301 shown in FIG. 1(b) is a strongsignal degree distribution of an imaging pattern of a mask pattern 104.The waveform 301 may be divided into a waveform 302 by the O-orderdiffraction light and a waveform 303 by high order diffraction light. Inthe case where the mask pattern 104 is a fine pattern 105 as shown, thewaveform 303 by the high order diffraction light is small with respectto the waveform 302 by the O-order diffraction light, and therefore, thewaveform 301 to be detected is small in contrast AM/AV. Since acomponent of the waveform 302 is removed by shielding the O-orderdiffraction light, the detected waveform is high in contrast as in thewaveform 302.

According to the Babinet principle, in diffraction patterns other thanthe O-order diffraction light, light from patterns adjacent to eachother is viewed as if phases of patterns adjacent to each other areinverted (deviated by π). That is, if the O-order diffraction light isshielded on the diffraction pattern, light to be imaged on the wafersurface is equivalent to one in which light from patterns adjacent toeach other in which as if phases are inverted (deviated by π) is imaged.At least a part of the O-order diffraction light is shielded by a shieldplate 324 (an imaging spatial filter 3302) at a diffraction imagesurface as shown in FIGS. 2 and 3 on the basis of the aforesaidtechnique, whereby only the diffraction light inverted in phase as shownin FIGS. 2 and 3 reaches the imaging surface, and therefore, thestrength distribution of the imaging surface is high in contrast.

A mechanism for enhancing a contrast will now be described. As anexample, FIG. 47 shows the transfer result of a circuit pattern formedon a mask shown in FIG. 46, and FIG. 48 shows a change in contrast whena pitch PIT, as shown in FIG. 46, is changed. In the conventionalreduction projection exposure method, a contrast rapidly goes down as apattern size becomes finer as indicated by curve 342, while in thereduction projection exposure method according to the present invention,it is understood that a contrast does not go down, as shown by curve341.

FIG. 49 shows an evaluation example of the focal depth in the reductionprojection exposure method according to the present invention. Accordingto the present invention, contrast indicates a value over about 80% inthe range of ±1.5 μm as indicated by curve 343. In the conventionalreduction projection exposure method, contrast rapidly drops due to adeviation of focal point as indicated by curve 344. This indicates thatit can correspond to a resist whose film is thick according to thepresent invention, and as a result, a wafer pattern with a resist at ahigh aspect ratio can be formed. As the result, a pattern with a resistwell retained at etching and with a high aspect ratio can be formed.

FIG. 14 shows a focal depth 362 of the present invention and a focaldepth 363 of the phase shifter method. Both the focal depths aresubstantially coincided. The focal depth 362 of the present inventionshows the excellent result as compared with the focal depth 361 of priorart.

FIG. 50 shows an embodiment of an excimer stepper which uses, as a lightsource, an excimer laser shorter in wavelength than the i-ray. Accordingto this embodiment, an excimer laser beam in the shape of a ring isscanned at a position of a light source spatial filter 3301 so that theeffect of the light source spatial filter 3301 can be achieved.Furthermore, according to this embodiment, the shape of the light sourcespatial filter 3301 can be easily controlled by controlling a scanningportion. That is, in this embodiment, as the light source portion 3100in the embodiment shown in FIG. 27, there is used an excimer laser whichuses gas such as KrF (krypton fluoride) having a shorter wavelength. Afurther fine circuit pattern can be transferred by using light having ashorter wavelength. Needless to say, in this embodiment, a laser havingother wavelengths can be used. In this embodiment, the light sourceportion 3100 comprises an excimer laser 3111, a shutter 3108, a beamexpander 3112, an X galvanomirror 3113, a Y galvanomirror 3114, anintegrator 3104, an integrator cooling arrangement 3120 and a condenserlens 3106. The spatial filter portion 3300 comprises a scan controlsystem 3311, a liquid crystal display element 3312 and a liquid crystalcontrol system 3313, and the light source filter regulating system 3303in the embodiment shown in FIG. 27 corresponds to the X galvanomirror3113, the Y galvanomirror 3114 and the scan control system 3311. Theintegrator cooling arrangement is adapted to prevent an increase intemperature of the integrator 3104 due to excimer laser lightconcentrated to the integrator. It is noted that the cooling arrangement3120 may be of a type to circulate cooling water or to spray nitrogengas for cooling. Other constituent elements correspond to those shown inFIG. 27. That is, in this embodiment, the position of the light sourcespatial filter 3301 is the position of the integrator 3104, and the Xgalvanomirror 3113 and the Y galvanomirror 3114 in the light sourcespatial filter regulating portion 3303 are scanned to thereby form aring-like light source having the same shape as that of the light sourcespatial filter 3301. In the imaging spatial filter 3302, a shieldportion is formed on the liquid crystal display element 3312 by theliquid crystal control system 3313 so as to have a shape which shields apart or the entirety of the O-order diffraction light as described inthe embodiment shown in FIG. 27. Accordingly, it is necessary that theresolving power of the liquid crystal display element 3303 hassufficient accuracy to form the above-described ring-like shape. Inaddition, an imaging spatial filter will suffice to be formed, andinstead of the liquid crystal display element, other elements, forexample, a metal plate formed so as to shield in a ring-like fashion orone in which a ring-like shield film is formed on glass may also beemployed.

Furthermore, an excimer laser beam is condensed at one point on theimaging spatial filter 3302. A ring-like shape is obtained on theimaging spatial filter first by the scanning on the light source spatialfilter in a ring-like fashion. If only respective points on the imagingspatial filter as well as the scanning on the light source spatialfilter are shielded, the object of the present invention can beachieved. Thereby, light is not excessively shielded, and there provideseffects that exposure time can be shortened, and the through-put can beincreased. The mask 100 is placed on the mask stage 3401, the mask stage3401 is controlled by the mask stage control system 3404, the mask 100is located to a reference position, a position of an alignment mark onthe wafer 200 is then detected by the locating mask detection portion3403, the wafer stage 3402 is controlled by the wafer stage controlsystem 3405 in accordance with the detected signal, and the mask 100 andthe wafer 200 are adjusted in position. After the adjustment ofposition, the shutter 3108 is opened, and a ring-like light source isformed by the light source spatial filter regulating portion 3303 sothat the mask 100 is illuminated and a mask pattern is transferred ontothe wafer 200 to form a wafer pattern.

In this embodiment, since the light from the excimer laser 3111 has ahigh coherence, this coherence need be decreased to an adequate value. Aring-like light source can be formed on the light source spatial filter3301 to thereby achieve the object simultaneously.

Particularly, in the present invention, it will suffice that uniformillumination can be made within an exposure field (within an exposurearea). The ring-like illumination in which a number of imaginary pointsources are arranged need not necessarily be illuminated simultaneously,but even if it is divided in time into plural numbers, scanning may beemployed as in the previous embodiment. It is also apparent that thering-like illumination in which a number of point sources are arrangedmay be divided into plural sections.

As described above, in the present invention, a large circuit patternportion and a small circuit pattern portion can be exposed twice.Further, a mask with a phase shifter arranged can be used on at least apart (or whole) of the circuit pattern on the mask. In this case, aring-like light source is used so that a center value of an incidenceangle of illuminating light incident upon a reticle is large, andtherefore, it is necessary to make a thickness of a phase shiftersomewhat thin in order that a deviation of phase caused by the phaseshifter is π. This value is calculated using an incidence angleaccording to expression (8).

    (2m+1)π≦(d/cos θ).(n/λ).2π       (8)

wherein m represents an integer, d represents a thickness of a phaseshifter, n represents a refractive index of the phase shifter, and λrepresents an exposure wavelength.

As described above, the present invention brings forth a new effect suchthat it can correspond to various circuit patterns by a conventionalexposure apparatus or a combination of a phase shifter and the like.

In carrying out the present invention, since the incidence angle oflight illuminated on the reticle is large, a problem arises in athickness of a circuit pattern such as chrome on the mask. Accordingly,it is desired that in carrying out the present invention, a thickness ofa circuit pattern such as chrome on the mask is made thin in order toobtain an accurate dimension of a transferred pattern. Accordingly, thefollowing expression (9) is required to be fulfilled.

    dm=pc/1                                                    (9)

wherein dm represents a thickness of a circuit pattern such as chrome,pc represents an allowance value of a transferred pattern, and 1represent a reduction rate of a reduction projection lens.

In order to realize this, it is necessary to perform patterning of amask with other materials which is lower in transmittance than that ofchrome. However, if the dimension of a circuit pattern of a mask isdetermined taking a variation of dimension caused by the incidence angleof illumination into consideration, the aforesaid problem can bereduced.

Furthermore, when a coating in which the transmittance of luminous fluxwhich is incident upon at a using incidence angle is maximum is appliedto the transmission portion of the mask, the exposure quantityincreases, enabling to reduce time required for exposure.

It is apparent that since the present invention makes use of thevibration property as mentioned above, it can be applied to an exposuredevice which uses an electron beam and X-rays.

According to the present invention, unbalance in light intensity betweenthe O-order diffraction light and the diffraction light can be avoidedwhen a mask pattern is transferred. The present invention has the effectthat exposure can be made with a resolving power equal to or more thanthat which uses a phase shifter by a conventional white and black maskpattern.

While we have shown and described several embodiments in accordance withthe present invention, it is understood that the same is not limitedthereto but is susceptible of numerous changes and modifications asknown to those skilled in the art and we therefore do not wish to belimited to the details shown and described herein but intend to coverall such changes and modifications as are encompassed by the scope ofthe appended claims.

What is claimed is:
 1. An exposure method comprising the steps ofilluminating a mask with light, and for imaging light one of transmittedthrough and reflected from the illuminated mask onto a substrate, thestep of imaging including at least partially inhibiting transmission oflight one of transmitted and reflected from the illuminated mask ontothe substrate.
 2. An exposure method comprising the steps of dividing acircuit pattern formed on a mask into a fine pattern portion and a largepattern portion, illuminating the mask with light, and imaging the lightone of transmitted through and reflected from the illuminated mask so asto transfer the fine pattern portion of the circuit pattern and thelarge pattern portion of the circuit pattern onto a wafer substrate forsemiconductor manufacturing.
 3. An apparatus comprising mask dataconversion means for converting and producing data of a mask from wiringdata, calculation means for applying arithmetic processing based on atransmission function substantially equal to a first imaging means fortransferring a circuit pattern formed on the mask using light withrespect to mask data obtained from the mask data conversion means andfor calculating data of the transferred pattern substrate.
 4. Anexposure apparatus according to claim 3, further comprising inspectionmeans including illuminating means for illuminating a mask with light,second imaging means for imaging light one of transmitted through andreflected from the mask illuminated by the illuminating means to adetection position, the second imaging means having a transmissionfunction substantially equal to the first imaging means, and lightreceiving means for receiving a pattern imaged on the detection positionto obtain an image signal, and comparison means for comparing an imagesignal obtained from the light receiving means of the inspection meanswith data of a transferred pattern on the substrate calculated by thecalculation means.
 5. An exposure apparatus, comprising:an illuminatingunit which illuminates a mask with light, said illuminating unitincluding a secondary light source having a transmitting portion oflight symmetrically disposed around a light axis on a ring-like area andat least a partially inhibiting transmission portion of light disposedinside of said ring-like area, said secondary light source beingprovided on a conjugate plane in relation to a spatial frequency region,said secondary light source including a light source spatial filtercontrol unit which controls a transmittance distribution of saidtransmitting portion in accordance with a spatial frequency of a circuitpattern formed on said mask; and an imaging system which images lightone of transmitted through and reflected from the illuminated mask ontoa substance.
 6. An exposure apparatus according to claim 5, wherein saidlight source spatial filter control unit selects dimension between saidlight axis and said transmitting portion.
 7. An exposure apparatusaccording to claim 5, wherein said light source spatial filter controlunit selects dimensions between an outside circle and an inside circleof said ring-like area.
 8. An exposure apparatus according to claim 5,wherein said light source spatial filter control unit selects atransmittance of said transmittance distribution.
 9. An exposureapparatus according to claim 5, further comprising an analyzing unitwhich analyzes said spatial frequency of the circuit pattern formed onsaid mask.
 10. An exposure apparatus according to claim 5, wherein theilluminating unit includes at least an excimer laser light source. 11.An exposure apparatus according to claim 5, wherein said imaging systemincludes a light transmission inhibiting system which at least partiallyinhibits transmission of light.
 12. An exposure apparatus according toclaim 11, wherein said light transmission inhibiting system forms aspatial filter.
 13. An exposure apparatus according to claim 5, whereinsaid imaging system includes a projection lens system.
 14. An exposureapparatus according to claim 5, wherein the mask is provided with acircuit pattern formed to have a line width substantially 1/2 of animage resolving power of the imaging system.
 15. An exposure methodcomprising the steps of:providing an illuminating system including asecondary light source having a transmitting portion of lightsymmetrically disposed around a light axis on a ring-like area and atleast a partially inhibiting transmission portion of light disposedinside of said ring-like area, said secondary light source beingprovided on a conjugate plane in relation to a spatial frequency region,said secondary light source including a light source spatial filtercontrol; controlling a transmittance distribution of said transmittingportion in accordance with a spatial frequency of a circuit patternformed on a mask; illuminating said mask with light obtained saidilluminating system; and imaging light one of transmitted through andreflected from said illuminated mask onto a substrate by an imagingsystem.
 16. An exposure method according to claim 15, wherein the stepof controlling the transmittance distribution of said transmittingportion comprises selecting dimensions between said light axis and saidtransmitting portion.
 17. An exposure method according to claim 15,wherein the step of controlling the transmittance distribution of saidtransmitting portions comprises selecting dimensions between an outsidecircle and an inside circle of said ring-like area.
 18. An exposuremethod according to claim 15, wherein the step of controlling thetransmittance distribution of said transmitting portion comprisesselecting a transmittance of said transmittance distribution.
 19. Anexposure method according to claim 15, further comprising the step ofanalyzing said spatial frequency of the circuit pattern formed on saidmask by an analyzing unit.
 20. An exposure method according to claim 15,wherein the step of illuminating comprises illuminating the mask with anexcimer laser light.
 21. An exposure method according to claim 15,wherein the step of imaging comprises inhibiting light transmission by alight transmission inhibiting system which at least partially inhibitstransmission of light.
 22. An exposure method according to claim 21,wherein said light transmission inhibiting system forms a spatialfilter.
 23. An exposure method according to claim 21, wherein saidimaging system includes a projection lens system.
 24. An exposure methodaccording to claim 15, wherein the mask is provided with a circuitpattern formed to have a line width substantially 1/2 of an imageresolving power of the imaging system.
 25. An inspection apparatuscomprising:an illuminating unit which illuminates a pattern on asubstrate with light, said illuminating unit including a secondary lightsource having a transmitting portion of light symmetrically disposedaround a light axis on a ring-like area and at least a partiallyinhibiting transmission portion of light disposed inside of saidring-like area, said secondary light source being provided on aconjugate plane in relation to a spatial frequency region; an imagingsystem which images light one of transmitted through and reflected fromthe illuminated pattern onto a detector; and a detecting unit whichdetects a defect by comparing a signal obtained by the detector with areference signal.
 26. An inspection apparatus according to claim 25,wherein said secondary light source includes a secondary light sourcespatial filter control unit which selects a transmittance distributionof said transmitting portion in accordance with a spatial frequency ofthe pattern formed on said substrate.
 27. An inspection apparatusaccording to claim 25, wherein said imaging system includes a lighttransmission inhibiting system which at least partially inhibitstransmission of light.
 28. An inspection method comprising the stepsof:providing an illuminating unit including a secondary light sourcehaving a transmitting portion of light symmetrically disposed around alight axis on a ring-like area and at least a partially inhibitingtransmission portion of light disposed inside of said ring-like area,said secondary light source being provided on a conjugate plane inrelation to a spatial frequency region, said secondary light sourceincluding a light source spatial filter control; illuminating a patternof a substrate with light obtained from said illuminating system; andimaging light one of transmitted through and reflected from theilluminated pattern onto a detector by an imaging system; and detectinga defect by comparing a signal obtained by the detector with a referencesignal.
 29. An inspection method according to claim 28, wherein said thesecondary light source includes a secondary light source spatial filtercontrol unit which selects a transmittance distribution of saidtransmitting portion in accordance with a spatial frequency of thepattern formed on said substrate.
 30. An inspection method according toclaim 28, wherein said imaging system includes a light transmissioninhibiting system which at least partially inhibits transmission oflight.
 31. An exposure apparatus, comprising:an illuminating unit whichilluminates a mask with light, said illuminating unit including a lightsource having a transmitting portion of said light and a transmissioninhibiting portion of said light disposed at least inside of saidtransmitting portion, said light source including a spatial filtercontrol unit which controls a transmittance distribution of said lightsource in accordance with a spatial frequency of a circuit patternformed on said mask; and an imaging system which images said circuitpattern onto a substrate by a light one of transmitted through andreflected from the light illuminated mask.